1. Field of the Invention
The present invention relates to an article transport device in which an article-retaining unit capable of retaining an article is provided to a moving body capable of moving along a guide rail on a ceiling, so as to be able to be raised and lowered to a raised position located close to the moving body and to a lowered position downward from the raised position, a housing space for housing an article retained by the article-retaining unit located at the raised position is formed on the moving body, an aperture for allowing the article-retaining unit to be raised and lowered between the raised position and the lowered position is formed in the lower-end region of the housing space, and purified air ventilation means for ventilating purified air in the housing space through an air purification filter is provided.
2. Description of the Related Art
In a case in which the article transport device described above transports an article from a transport-origin article transport point to a transport-destination article transport point, first, the moving body moves to a stop position corresponding to the transport-origin article transport point and lowers the article-retaining unit from the raised position to the lowered position, and the article-retaining unit located at the lowered position receives the article from the article transport point. Thereafter, the article transport device raises the article-retaining unit from the lowered position to the raised position and, while the article is retained by the article-retaining unit located at the raised position, the moving body moves to a stop position corresponding to the transport-destination article transport point and lowers the article-retaining unit from the raised position to the lowered position, and the article-retaining unit located at the lowered position hands off the article at the transport-destination article transport point.
The article transport device thus transports articles among a plurality of article transport points by using the moving body to move from position to position and by raising and lowering the article-retaining unit. Such an article transport device is used to transport an article among a plurality of article transport points in, for example, a cleanroom, the article transport points being article processing units for carrying out various processes on the article. Accordingly, there is a desire to maintain clean conditions for the article during the transport thereof as well.
In view of this, in a conventional article transport device, a housing space for covering the periphery of an article retained by an article-retaining unit located at the raised position is formed on the moving body, and purified air ventilation means for ventilating purified air in this housing space through an air purification filter is provided (for example, see JP-B 3226017). Purified air is thereby ventilated to the article housed in the housing space when the article-retaining unit is located in the raised position and the moving body is used for movement, and the article being transported is kept in clean conditions.
In the above-described device recited in JP-B 3226017, the housing space is formed in a rectangular shape, and a clean unit having an air-blowing fan and an air filter through which the airflow generated by this air-blowing fan passes is provided as the purified air ventilation means. The clean unit is disposed such that the clean airflow that has passed through the air filter blows out into the housing space from substantially the entire area of one lateral surface of the housing space (a lateral surface on the front side of the moving body in the direction of travel). To supply a clean airflow to the entire article inside the housing space, the housing space is provided with a flow-regulating plate for guiding the clean airflow to the surface opposite from the clean unit, and the surface in the housing space facing the clean unit is provided with a plurality of fins for regulating the flow direction of the clean airflow, spaced out at intervals in the up-down direction.
In an article transport device as described above, raising and lowering the article-retaining unit between the raised position and the lowered position allows articles to be exchanged (i.e., received and delivered) between the article-retaining unit and an article transport point such as an article processing unit. Therefore, an aperture for allowing the article-retaining unit to be raised and lowered between the raised position and the lowered position is formed in the lower-end part of the housing space. Dust therefore sometimes infiltrates into the housing space from outside the housing space through the aperture, and this dust sometimes adheres to the article housed in the housing space.
In view of this, in the above-described device according to JP-B 3226017, dust is prevented from infiltrating into the housing space from outside the housing space through the aperture by providing the plurality of fins for regulating the flow direction of the clean airflow and forming an air curtain for shielding the aperture. However, for example, the occurrence of even slight disturbance to the airflow may allow dust to infiltrate into the housing space through the aperture, which is a concern. It is therefore difficult to prevent dust from infiltrating into the housing space through the aperture merely by forming the air curtain.
In a case in which the article to be transported is, for example, a reticle cassette that houses a reticle for the lithographic exposure of semiconductors, liquid crystal display panels, or the like, a substance such as ammonia or sulfur dioxide may infiltrate into the housing space through the aperture and this substance adheres to the reticle cassette, creating a possibility that a cloudiness termed “haze” will occur in the reticle (that is, the reticle will become opaque), and the quality of the reticle will be adversely affected. In view of this, there is a need to prevent a substance such as ammonia or sulfur dioxide from adhering to the reticle cassette, but because an air curtain is merely formed in the above-described device recited in JP-B 3226017, it is difficult to prevent a substance such as ammonia or sulfur dioxide from infiltrating into the housing space from aperture.
The following is an additional description regarding the occurrence of haze (cloudiness) when a substance such as ammonia or sulfur dioxide adheres to a reticle cassette.
The reticle cassette serving as the article to be transported comprises, for example, a cassette body and a lid body that can be mounted onto the cassette body and can be removed from the cassette body. Further, for example, with a reticle being supported on the backside of the lid body and the lid body being mounted onto the cassette body, the reticle is housed in an enclosed space formed within the reticle cassette, and the reticle is kept in clean conditions. The reticle is used to perform lithographic exposure and other processes at the article processing unit serving as the article transport point. Therefore, the reticle is exchanged between the article processing unit and the article-retaining unit lowered to the lowered position. In this exchange of the reticle, it is not that the reticle itself is exchanged, but rather that the part of the reticle cassette supporting the reticle, such as the lid body, is exchanged as a unit. Accordingly, a part of the reticle cassette is transported to the article processing unit. Therefore, ammonia, sulfur dioxide, or the like in the air adheres to this single part of the reticle cassette, whereupon light energy is applied when lithographic exposure or another process is performed, and the ammonia, sulfur dioxide, or the like initiates a chemical reaction, generating ammonium dioxide or other haze-causing substances. Haze thus occurs when a substance such as ammonia or sulfur dioxide adheres to the reticle cassette.